There is a speaker unit stored in a tire storage unit formed in a vehicle to be used (for example, refer to Patent Documents 1 and 2).
Such speaker unit is often used as a unit referred to as a woofer which outputs low-register sound.
The speaker unit disclosed in Patent Document 1 is stored in the tire storage unit from which a spare tire is removed, and the speaker unit is stored in an appropriate state regardless of a size of the tire storage unit through adjustment of an amount of air filled in an air sac inflated by filled air.
The speaker unit disclosed in Patent Document 2 is stored in a space opening upward formed on a central portion of the spare tire stored in the tire storage unit.